Permanent magnet objective lenses for multicolumn electron-beam systems

Abstract

This article presents permanent magnetic objective lenses suitable for use in multicolumn electron-beam systems. Two types of lens arrays are presented, a single-pole lens tip array, and a multibore immersion lens array. Prototype lenses were tested as add-on lens attachments on an existing scanning electron microscopy (SEM), by mounting them on to the specimen stage of a conventional SEM, and successively moving each tip/bore on to the optical axis. SEM images were obtained from 2 by 2 tip/bore arrays. The images have demagnification strengths varying from 1000 to 7000 and are obtained from specimen regions up to 16 mm apart. These results demonstrate that permanent magnet multibeam objective lenses are in principle feasible. The axial field distribution created by each tip/bore in these multibeam lenses is similar to the axial field distribution of a single tip/bore high-resolution immersion lens.